1. Field of the Invention
The present invention relates generally to walk-assist and power generation devices and methods, and more particularly, to devices, which generate power and/or assist movement when worn.
2. Prior Art
During walking on a flat, rigid and horizontal surface, a human subject spends energy and tires. On the other hand, if the human subject were instead riding a bicycle that is in good condition, the subject has to spend a significantly less amount of energy to travel the same amount of distance. And in general, the faster the person walks (or runs), the difference between the amount of energy that has to be spent to travel a certain distance on foot or on bicycle becomes greater. The reason for this significant difference in the amount of energy that a person has to spend to travel a certain amount of distance can be described as follows. Here, the objective is to account for the major sources of energy expenditure and for the secondary and generally less significant but complex processes that demand energy expenditure during locomotion.
During normal walking (gait), there are two main sources of energy expenditure. Firstly, due to the structure of the human body, energy is spent to sequentially accelerate and decelerate the lower limbs and to a lesser degree certain other parts of the body (e.g., pumping arms) to achieve locomotion. This component of the energy spend by a person during the process of locomotion is hereinafter called the “locomotion energy”. This is the case even during a highly efficient mode of locomotion along a straight path in which the trunk moves at a nearly constant velocity. During normal walking, the motion of the lower limb is nearly periodic. During each cycle of gait, the muscles acting on the lower limbs are responsible for both accelerating and decelerating the limb segments. The muscles consume energy to apply the forces required to accelerate the limb segments and they consume energy to apply the forces required to decelerate the limb segments. In comparison, if the person were riding a bicycle, following initial acceleration to a constant travel velocity, the person has to provide minimal energy to the human-bicycle system since no significant inertia has to be sequentially accelerated and decelerated (neglecting the small friction forces, aerodynamic drag, etc.).
Secondly, muscle forces have to provide the required forces across the various joints of the lower extremities and the back and neck to keep the body upright (or on the seat of the bicycle) and to provide for a stable posture. Thereby the person has to spend energy to provide such muscle forces. This component of the energy spent by a person during the process of locomotion is hereinafter called the “stance energy”. The amount of energy required for this purpose is usually significantly higher than the required minimum since the muscle groups generally act together and provide opposing (isometric) forces that provide joint preloads that in turn provide for extra stability margin.
Thus, in order to more significantly reduce the amount of energy that a person has to spend during locomotion, the amount of aforementioned “locomotion energy” and “stance energy” that is consumed by the muscles has to be reduced. Currently, certain devices are known in the art that are used to reduce joint loads and/or to reduce muscle forces (mostly in the lower extremities) that are required for stance stability. These devices do reduce the “stance energy”, some a very small amount and some slightly more, and are discussed below. There is, however, no device currently available for directly reducing the “locomotion energy”.
To provide or supplement muscle forces in achieving a stable stance, various assist or support devices have been developed. Such stance or support assist devices generally help to reduce the muscle forces that are required to keep the body upright and to provide stance (sitting) stability. As a result, such devices also help reduce the aforementioned “stance energy” requirements during locomotion to various degrees. A person may use one or more of such assist or support devices due to the lack of adequate muscle force levels or control due to age, joint disease, soft or hard tissue injury or operation, etc. These devices include various braces, walkers, canes, crutches, and the like. As a result, the forces that the muscles have to provide and the forces across the various joints of the lower extremities are generally reduced. The currently available assist devices may be divided into the following two categories. Here, various shoe inserts, components incorporated into the shoes, etc., are not considered since they are primarily used to modify force distribution on the foot and its joints by providing certain type of interface between the foot and the shoe (ground).                1. Various bracing devices used to bridge one or more joints, for the primary purpose of reducing the load transmitted through the joint. The level of muscle forces that act across the joint to provide joint stability is also reduced, thereby further reducing the joint forces. Depending on the effectiveness of the bracing in providing joint (stance) stability, the “stance energy” is reduced by a certain amount.        2. Various walk assist devices such as walkers, canes, crutches, etc., for the primary purpose of reducing load on one or both lower extremities. When such assist devices are used, other muscles, usually the arm and shoulder and certain upper body muscles, must then provide the forces needed to assist stance stability and locomotion. The person obviously has to spend energy to provide the latter muscle forces. The currently available assist devices do not significantly reduce the total stance energy expended but merely transfer the load from the lower limb muscles to the muscles of the arm and the upper body.        